Biosynthesis of the pipecolate moiety of marcfortine A

In this paper, we demonstrate that the marcfortine A (MA) producing Penicil lium strain incorporates L-lysine, which is metabolized to the pipecolate m oiety by losing the alpha-amino group and not the E-amino group as determin ed by employing [alpha-N-15]- or [epsilon-N-15]-L-lysine in our feeding stu dy. Each of the enriched samples was analyzed by FAB-MS and a number of NMR experiments. The analysis of the H-1 NMR spectrum allowed us to estimate t he absolute enrichment of the amide nitrogen (N-beta). Analysis of HMBC spe ctra allowed us to establish the relative enrichments of the other two nitr ogens to N-beta. To the best of our knowledge, this represents the first ti me that results from an HMBC experiment have been used to quantitate the re lative enrichment of an isotope. The agreement between NMR results and the FAB-MS are excellent, further supporting our conclusions. The knowledge of the specific loss of the alpha-amino group allows the differentiation of tw o plausible pathways in converting L-lysine to pipecolic acid.